Arrangement in air blast circuit breakers in which drying air is delivered to the control air pipe



June 9, 1959 H. FORWALD- 2,890,312

' ARRANGEMENT IN AIR BLAST CIRCUIT BREAKERS IN WHICH DRYING AIR Is DELIVERED TO THE CONTROL AIR PIPE Filed Sept. 5, 1957 IN VEN TOR.

Haak on Tom/a Z d United States Patent ARRANGEMENT IN AIR BLAST CIRCUIT BREAK- ERS IN WHICH DRYING AIR IS DELIVERED TO THE CONTROL AIR PIPE Haakon Forwald, Ludvika, Sweden, assignor to Allmanna Svenska Elektriska Aktiebolaget, Vasteras,

Sweden, a Swedish corporation Application September 5, 1957, Serial No. 682,174 Claims priority, application Sweden October 11, 1956 Claims. (Cl. 200-148 In an air blast circuit breaker the control 'air pipe is commonly empty, i.e. the pressure is one atmosphere in the air pipe when the circuit breaker is in its closed position. In order to prevent the possibility of condensing water seriously lowering the insulating property inside the control air pipe, drying air is continuously delivered to it. This air can be delivered from a compressed air container through a capillary tube the length and diameter of which determine the quantity of air delivered. By the expansion, the relative moisture of the delivered drying air decreases, so that the air will be able to take up and carry away moisture from the air pipe.

The quantity of air necessary to keep the air pipe dry is very small and the air supply can be fixed by using a capillary tube as a pressure reducing valve. The air consumption can however be increased by leakage at the operating valve of the circuit breaker or by leakage at joints in the control air pipe when the control air pipe is arranged inside a pillar insulator filled with compressed air. In order to prevent unnecessary air consumption it is advantageous to indicate when excessive quantities of air are streaming into the control air pipe.

The present invention relates to an arrangement in air blast circuit breakers, in which drying air is delivered to the control air pipe of the circuit breaker through a capillary tube and in which means for indicating leakage of air to said control air pipe is arranged. The invention is mainly characterised in that the drying air leaves the control air pipe through a restricted outlet opening, so that the pressure inside said pipe is dependent on the air quantity streaming into it, and in that pressure indicating means connected to the control air pipe is arranged to indicate the pressure in said control air pipe and to give a signal when the pressure has reached a certain predetermined value because of air leakage to said pipe. The restricted outlet opening may consist of a nozzle through which the control air pipe permanently communicates with the atmosphere. In order to prevent air from streaming into the pipe if the drying air supply should be stopped, a back valve may be arranged between the outlet opening and the atmosphere or the control air pipe.

In the accompanying drawing one embodiment of the invention is shown, and the arrangement includes a container 1 filled with compressed air. This container carries a pillar insulator 2 upon which a connecting member 3 is arranged. This member 3 carries two extinguishing chambers 4, which through the annular channel 5 inside the pillar insulator 2, permanently communicate with the compressed air container 1. The operating mechanism of the extinguishing chambers may be connected to the container 1 by means of the valve device 6 and the control pipe 7. The control air pipe 7 is arranged inside the pillar insulator 2 and consists partly of an insulating pipe 8. At the upper part of the control air pipe in the connecting member 3 a restricted outlet opening 9 is arranged. Outside this opening there is a valve member 10, which is movable between an upper 2,890,312 Patented June 9, 1959 valve seat 11 and a lower valve seat 12. This valve member is actuated by a spring 13 against the lower valve seat 12. The valve device 6 at the lower part of the control air pipe contains an operating rod 14 and attached to said rod a valve disc 15 which closes the opening 16 between the control air pipe 7 and the container 1, and a valve disc 17 is movable upon the rod 14 and closes the opening 18 between the control air pipe and the atmosphere. When the opening 16 between the control air pipe 7 and the container 1 is closed by the valve disc 15 a spring 19 presses the valve disc 17 against its seat but when said opening 16 is open the collar 20 upon the rod 14 presses the valve disc 17 against its seat by a force transmitted from the opera-ting piston 21 in the cylinder 22. Said piston 21 is actuated in one direction of the spring 23 and may be actuated in the other direction by compressed air supplied to the cylinder 22 through the pipe 38. Drying air is delivered to the control air pipe 7 through the pipe 24, the filter 25 and the capillary tube 26. The stream of drying air is directed against the shield 27 and thus actuate-s the contact bridge 28 in the direction away from the contacts of the breaking gap 29 in the signal circuit 30. The device 31 is a pressure indicating device, which is influenced by the pressure in the control air pipe. In this device there is a breaking gap 32 of a signal circuit 33 and a movable contact bridge 34, connected to the piston 35 of the indicating device. The piston 35 is actuated in one direction of the spring 36 and in the opposite direction of the pressure in the control air pipe.

The arrangement operates in the following Way. When the breaking gaps of the extinguishing chambers are closed, the pressure of the control air pipe only slightly exceeds the atmospheric pressure. Drying air streams from the air container 1 through the pipe 24 and the capillary tube 26 into the control air pipe and hits the shield 27 so that the breaking gap 29 of the circuit indicating faults is held open. The drying air which, by its expansion has a relatively low percentage of moisture, passes through the control air pipe 7 and streams out through the restricted outlet opening 9. During its passage through the pipe the air absorbs moisture and thus keeps the walls of the pipe dry. In the control air pipe, a small excess of pressure is maintained, and the value of this excess pressure depends on the area of the restricted outlet opening 9 and the quantity of air delivered to the control air pipe. With normal pressure in the control air pipe the breaking gap 32 is open. If the quantity of air, coming into the control air pipe increases for instance because of a leakage at the valve disc 15, or because of leakage at the joints at the ends of the tube 8 the pressure in the conduit 7 increases. The piston 35 then moves the contact bridge 34 to the left so that the breaking gap 32 is closed and a signal is given.

The valve between the restricted outlet opening 9 and the atmosphere is not absolutely necessary but is mostly very favorable. In its lower position the valve member 10 prevents air from streaming into the control air pipe through the opening 9. When the control air pipe, through the opening 16, communicates with the compressed air container 1, the pressure increases in said pipe. The quantity of air escaping through the opening 9 increases and lifts the valve member 10 up to the valve seat 11, and thus prevents air from streaming out from the control air pipe when the breaker is open and the pipe is under operating pressure. 37 indicates a breaking gap in a signal circuit, which suitably is opened when operating air is delivered to the control air pipe. The opening of this breaking gap 37 prevents the signal lamps from being switched on when the breaking gaps 29 and 32 are closed because of operating pressure in thecontrol air pipe but thehigh pressure does not cause faults in the circuit breaker.

The invention is not limited to the embodiment shown in the figure. The design may of course be varied in many ways within the scope of the invention.

I claim as my invention:

1. An air blast circuit breaker comprising a control air pipe for the delivery of drying air, a tube device for the admission of the drying air to the control air pipe, a restricted outlet opening for the passage of the 10 drying air from the said pipe so that the air pressure in the pipe depends upon. the volume of the air delivered thereto, and pressure indicating means in communication with the air pressure in said pipe for signalling when the said air pressure exceeds a predetermined, value.

2. A circuit breaker according to claim 1, in which the saidtube device includes a capillary tube.

a valve arranged in series with said outlet opening. and,

means for closing said valve when the control pipe is filled with operating air.

References Cited in the file of this patent UNITED STATES PATENTS Adams Aug. 7, 1906 Forwald June 23, 1953 

